As onshore oil and gas resources are depleted gradually, the exploitation of offshore oil and gas resources has received more and more attention. Especially, deep-water oil and gas resources will be the key in exploration and exploitation, owing to their high reserve. Deep-water well drilling is different from shallow-water drilling and onshore drilling: the low-temperature and high-pressure deep-water environment, generation of hydrates, and existence of shallow gas sharply increase risk of gas kick and well blowout during deep-water well drilling and have strong impacts on the safety and time efficiency of the drilling operation; in deep sea areas, where high-permeability reservoir beds exist, gas kick may happen more easily, and more severe accidents may occur if the gas kick turns to well blowout. In the past, more attention was paid to the research on the mechanism of gas kick and the blowout control method in the well drilling process. Actually, in the process of drilling stop, waiting on cement, and well shutdown for protection against typhoon, etc., there is also a risk of gas invasion into the wellbore. For example, a well blowout and oil spill accident happened in the “Deepwater Horizon” oil rig in the Gulf of Mexico in 2010. Thus, it can be seen that gas kick prevention and control in different deep-water well drilling processes has become a major challenge to be solved in the exploitation of deep-water oil and gas resources. The mechanism of gas invasion into the wellbore and the gas bubble migration mechanism in the wellbore must be studied on the basis of the characteristics of gas kick to obtain a well kick control theory.
The mechanism of gas invasion and migration during shutdown of deep-water oil and gas well is difficult to accurately describe with the existing theory; in addition, most conventional experiments on the gas invasion and migration mechanism are made at normal temperature and normal pressure, and can't truly simulate deep-water environment and reservoir bed conditions. Hence, it is necessary to design an experimental apparatus that simulates the gas invasion and migration process during shutdown of a deep-water oil and gas well with reference to the wellbore temperature and pressure, and reservoir bed characteristics in deep-water, and use the experimental apparatus to study the mechanism of strata gas invasion into wellbores and the mechanism of gas bubble migration, merging and/or phase transition in wellbores, in order to provide an experimental basis for establishing a theoretical model of gas kick and thereby provide theoretical support for safe and efficient offshore deep-water well drilling.